Correlating Heterogeneities in Support Fragmentation to Polymer Morphology in Metallocene-Based Propylene Polymerization Catalysis

Abstract

In the field of olefin polymerization catalysis, metallocenes are heterogenized with methylaluminoxane onto silica supports to yield active catalysts. During olefin polymerization, these silica supports act as a framework to control the fragmentation stage, thereby influencing the final polymer product and preventing reactor fouling and fines formation. This study investigates the influence of different silica supports induced on the final polymer product. To study a broad range of silica supports from an industrial silica database, we utilize a hierarchical clustering method to cluster the supports based on their physical properties. From the clustering method, five supports representing the clusters and an industrial benchmark were analyzed at different polymerization stages using focused ion beam–scanning electron microscopy (FIB–SEM) and microcomputed tomography (microCT). This combined FIB-SEM/microCT methodology revealed differences in both fragmentation behavior and polymer morphologies based on structural features, including macropores, mesopores, spray-dried shells, spray-dried spheres, and denser shells. The heterogeneity and ideal fragmentation behavior was further assessed by calculating the replication factor of each support, indicating that silica materials containing macropores and spray-dried shells have an almost ideal replication phenomenon. This multiscale analysis revealed new understanding of catalyst fragmentation for different supports. This understanding could in the future be further developed by the addition of more supports or additional analysis of the supports to the industrial database.